WASHINGTON 
Mexican drug cartels are creeping south into Central America, U.S. drug enforcement officials said Wednesday, as the Obama administration put new pressure on drug kingpins ahead of the president's trip to Mexico City. Drug Enforcement Administration officials said there are growing signs that stepped-up law enforcement efforts on the U.S.-Mexico border are driving the cartels south toward Central America.

"We're looking at what happens south of Mexico as well, because that's just as important as what's happening on our border," said DEA Chief of Operations Thomas Harrigan. "With more and more success the Mexican government has, literally they're pushing these cartels further south and potentially it could be a problem in Central America."

There have been significant seizures of cartel weaponry in Guatemala, and shootouts among Mexican cartels with operations in Central American countries. The cartels "definitely have" moved south, said Placido.

"We've seen running gun battles in places like Guatemala and Honduras between rival Mexican cartels," he said.

Last month in an appearance before Congress, U.S. State Department official David Johnson said that Central American officials "have identified gangs, drug trafficking and trafficking of arms as the most pressing security concerns in that region."

The acting head of the DEA, Michele Leonhart, told reporters that more efforts along the U.S.-Mexico border alone will not be enough to dismantle the cartels.

"A seizure on the border is not going to break the backs of the cartels. What breaks the backs of the cartels are the partnerships with the U.S. and Mexican counterparts in country, in Mexico," she said.

Homeland Security Secretary Janet Napolitano said the DEA's assessment on the cartels moving south is a serious concern. She said the violence moved based in part on enforcement on both sides of the U.S.-Mexico border.

"It is an ever-changing environment that we have to face," she said.

Napolitano spoke in El Paso, Texas, where she announced she has picked Alan Bersin, a former federal prosecutor, to take the new post of "border czar" to oversee efforts to end cartel violence along the border and slow the tide of people crossing illegally into the United States.

Separately, the White House on Wednesday announced that three Mexican organizations had been added to a list of suspected international drug kingpins: the Sinaloa cartel, Los Zetas and La Familia Michoacana.

The move came a day before President Barack Obama travels to Mexico.

The three Mexican groups were added to the U.S. government's blacklist of drug syndicates, known commonly as the Drug Kingpin Act and aimed at financially cutting off significant foreign narcotics traffickers, their organizations and operatives worldwide.

Those on the list are denied access to the U.S. financial system and all trade and transactions involving U.S. companies and individuals.

La Familia Michoacana, also known simply as La Familia, moves massive amounts of cocaine from Colombian drug dealers, according to U.S. officials.

Los Zetas was formed by ex-military men who became hit men for the other cartels.

The Sinaloa cartel, often referred to as the Mexican Federation, began in the 1970s and now controls most of the seaports along the Pacific coat of Mexico, officials say.

The president has already promised to dispatch nearly 500 more federal agents to the U.S.-Mexico border, along with X-ray machines and drug-sniffing dogs.